The present invention relates to a seat-belt arrangement incorporating a seat-belt and a force limiter.
It has been proposed to use force limiters, and in particular energy-absorbing force limiters, in connection with safety devices provided in motor vehicles such as, for example, seat-belts. The function of a force limiter is to yield, whilst absorbing energy, if the force limiter is subjected to a force in excess of a predetermined threshold. Whilst it is always desirable to ensure that an occupant of a vehicle should not accelerate or decelerate substantially with reference to the vehicle during an accident situation, it is known that it is undesirable to apply excessive forces to the torso of an occupant through a seat-belt in order to achieve this objective, since the application of high forces may injure the occupant of the vehicle. Thus, the effect of a force limiter is such that when a very substantial acceleration is to be imparted to a vehicle occupant by a safety-belt, the safety-belt will yield slightly, whilst the force limiter absorbs energy, thus minimizing the risk of injury arising.
Various types of force-limiting energy-absorbers have been proposed previously, including energy-absorbers which rely on the deformation of a metal element. Such arrangements are relatively simple and have a very predictable operating characteristic, but suffer from the disadvantage that it is not easy to vary the level of energy absorbed in response, for example, to the weight of the occupant of the seat or the position of the occupant of the seat immediately before commencement of the accident.
The energy absorbed by a force limiter as used in the context of a safety-belt in a motor vehicle is rather high, and thus many systems are relatively complex.